Huh, so I'm only just learning that the Snellen chart isn't the common one! I wouldn't have known the name of it, but if someone asked me to doodle an eye chart from memory, I would've drawn that blocky E with the serifs! I've most likely been tested with the sans-serif Sloan chart I assume, but the letter forms just aren't distinct enough to stick in my brain I guess. A bit of a shame this font doesn't have a "Optician Serif" variant to look like the Snellen letters.